This invention relates to the production of electrically conductive polymer materials and is particularly concerned with the production of such materials exhibiting high thermal stability, and with procedure for producing same.
The free-base form of polyaniline, that is, polyaniline free of acid groups, is believed to comprise subunits having the formula: ##STR1## where x is between 0 and 1. The oxidation state of polyaniline referred to as "emeraldine" is believed to have a value of x of about 0.5.
The free-base form of polyaniline is electrically non-conductive. Protonic acid doping of polyaniline by reaction of polyaniline with a protonic acid HX where X is, for example, Cl, to produce electrically conductive polyaniline is known, for example, as disclosed in A. G. MacDiarmid, et al, Mol. Cryst. Liq. Cryst. 121, 173 (1985). Conductive polyaniline of this type has been employed in batteries, as disclosed, for example, in French Pat. No. 1,519,729.
However, a number of difficulties have been encountered with such prior art electrically conductive materials. Some of these problems were addressed in U. S. Applications Ser. No. 920,474 filed Oct. 20, 1986, of S. I. Yaniger, now U.S. Pat. No. 4,798,685, and Ser. No. 013,305 filed Feb. 11, 1987, of S. I. Yaniger, et al, now U.S. Pat. No. 4,806,271, both assigned to the same assignee as the present application. In these applications, it is disclosed that Lewis acids, for example, alkylating agents, can be used to make the insulating emeraldine free-base into a conductive polymer salt. Use of proper Lewis acids resulted in conductive polyanilines with the Lewis acid as a sidechain.
Thus, in the above U. S. application, Ser. No. 920,474, a base-type non-conductive polymer, such as polyaniline, can be reacted with, for example, methyl iodide, to form an electrically conductive polymer in which the methyl group is covalently linked to the nitrogen atoms of the polymer.
In the above U. S. application, Ser. No. 013,305, emeraldine free-base can be reacted with reagents of the form RS.sub.2 Cl, e.g., tosyl chloride, to form an electrically conductive polymer in which the --SO.sub.2 R cation groups are covalently linked to the nitrogen atoms of the polymer.
However, polymers of the above applications exhibit loss of conductivity when exposed to high temperatures. For example, the conductive polymer produced by emeraldine free-base treated with tosyl chloride (conductivity =1.0 S/cm) loses its conductivity when heated to 150.degree. C. for one hour. The thermal instability results from interaction of the relatively nucleophilic chloride counterion with the amine bound hydrogens of the polymer backbone.
An object of the present invention is the provision of improved base-type electrically conductive polymers of the class of conductive polyaniline.
Another object is to provide conductive polymers, such as conductive polyaniline, having thermally stable counterions in the conductive polymer system.
Still another object is the provision of a conductive base-type polymer of the above type, such as conductive polyaniline, having groups which are thermally stable and remain bound to the nitrogen atoms of the polymer even at high temperatures and which increase the oxidative stability of the polymer backbone.
Yet another object is to provide novel procedure for producing the above conductive polymers.